Gasoline Homogeneous Charge Research Articles

Effects of water direct injection on a combustion phase and performance of six-stroke gasoline homogeneous charge compression ignition engine

An experimental study was conducted to examine how direct water injection (WI) can optimize the combustion phases of a six-stroke gasoline homogenous charge compression ignition (HCCI) engine. With six-stroke HCCI combustion, the limitations of four-stroke HCCI combustion under high loads and the stability of combustion under low loads can be resolved by adding additional compression and expansion stroke. Previous six-stroke HCCI combustion research suggested that the time loss could be reduced by delaying the combustion phase to the top dead center (TDC) with additional cooling. Thus, in this study, the effects of WI on the overall pressure curve, as well as the first and second combustion phases, were studied from a thermal and chemical kinetics perspective. The performance, thermal efficiency, and pressure rise rate were also examined. It was found that WI retarded the first and second combustion. The first and second combustion phases were located after and before TDC, respectively, resulting in a decrease in the first gross mean effective pressure (GMEP) (180–540 CA) and an increase in the second GMEP (540–900 CA). Because the increase of second GMEP was dominant, the indicated thermal efficiency also monotonically increased (2.7–3.5%p). In addition, the maximum pressure rise rate decreased by 23.1% to 65.2%. Thus, the WI can be used to control the combustion characteristics of six-stroke gasoline HCCI engine.

Enhancing the efficiency benefit of thermal barrier coatings for homogeneous charge compression ignition engines through application of a low-k oxide

Prior experiments reported by the authors have proven the hypothesis that achieving a dynamic temperature swing on the combustion chamber surface will lead to improved thermal and combustion efficiencies of the homogeneous charge compression ignition engine. A thin layer of yttria-stabilized zirconia, roughly 150 μm, was plasma sprayed on the piston top. It led to markedly advanced ignition and heat release in the gasoline homogeneous charge compression ignition engine, accompanied with reduced unburnt hydrocarbon and carbon monoxide emissions, improved combustion efficiency, and a higher thermal efficiency. A related computational study highlighted the critical role of coating thermal conductivity in achieving a desired dynamic response; hence, the second phase of experimental investigations focused on introducing structured porosity in the yttria-stabilized zirconia coating, as a means of reducing effective conductivity. Indeed, additional incremental improvements were observed, as well as limitations related to adverse effects of the surface roughness and the fuel interactions with the surface roughness and open pores. Erosion can also be a problem in a direct injection engine. Therefore, the third round of investigations focused on a material with a natively low conductivity (low-k), sprayed on the top of an Al piston in a relatively dense form, and in a way that yields a smooth surface. The objective was to capitalize on the low conductivity, while avoiding the pitfalls accompanying high-porosity formulations. The heat-storage capacity was limited by keeping the thickness relatively low. The results verify the paramount importance of thermal conductivity in the context of high “temperature swing” behavior and indicate a potential to improve the homogeneous charge compression ignition engine’s combustion efficiency roughly 1.5%, with the overall indicated efficiency improvement on the order of 5%, on a relative basis. In addition, the low-k oxide thermal barrier applied to the piston extended significantly the low-load homogeneous charge compression ignition operability limit.

Numerical study on the approach for super-high thermal efficiency in a gasoline homogeneous charge compression ignition lean-burn engine

The approach for achieving super-high thermal efficiency in a gasoline homogeneous charge compression ignition lean-burn engine was studied using numerical simulation. A model engine was designed based on the split cycles, including the low-pressure cycle consisted of the turbocharger system and the high-pressure cycle controlled by the variable effective compression ratio ( ε) and the exhaust gas recirculation (EGR). Based on the model engine, load (L) – Φoxy (F) – EGR (E) – ε (E) cooperative control strategy was proposed to optimize the thermal efficiency and its interactive mechanism was clarified. The results revealed that the core of the load (L) – Φoxy (F) – EGR (E) – ε (E) strategy was the simultaneous optimization of the combustion process and the specific heat ratio ( γ) contributing to the piston work maximization. The optimum combustion phase was found in the range of 4°–9° crank angle after top dead center, and highest combustion rate under the rough combustion restriction was also required. Under this precondition, reducing ε to retard the combustion phase appropriately could mitigate the EGR usage to improve the γ. Based on the load (L) – Φoxy (F) – EGR (E) – ε (E) strategy, increasing the load was found to improve the thermal efficiency effectively by reducing the heat transfer loss. The highest brake thermal efficiency of 50% was reached when the gross indicated mean effective pressure was increased to 15 bar under the conventional engine condition. Further increasing the gross indicated mean effective pressure to 35 bar with elevated peak cylinder pressure of 400 bar could improve the brake thermal efficiency to 54% under the enhanced mechanical strength condition. To pursue super-high thermal efficiency, the approach of thermal insulation for the engine was proved to be more effective. It showed the potential to achieve the super-high brake thermal efficiency over 60% and maintain clean combustion by adopting the load (L) – Φoxy (F) – EGR (E) – ε (E) strategy in the model engine with thermal insulation and high mechanical strength.

Experimental investigation of the relationship between thermal barrier coating structured porosity and homogeneous charge compression ignition engine combustion

Heat transfer has a profound influence on homogeneous charge compression ignition combustion. When a thermal barrier coating is applied to the combustion chamber, the insulating effect magnifies the wall temperature swing, decreasing heat transfer during combustion. This enables improvements in both thermal and combustion efficiency without the detrimental impacts of intake charge heating. Increasing the temperature swing requires coatings with lower thermal conductivity and heat capacity. A promising avenue for simultaneously decreasing both thermal conductivity and capacity is to increase the porosity fraction. A proprietary solution precursor plasma spray process enables discrete organization of the porosity structure, called inter-pass boundaries, which in turn produces a step-reduction in thermal conductivity for a given porosity level. In this investigation, yttria-stabilized zirconia is used to create four different thermal barrier coatings to study the potential of structured porosity as means of improving the “temperature swing” behavior in a homogeneous charge compression ignition engine. The baseline coating is “dense YSZ,” applied using a standard air-plasma spray process. Next, significant reductions of the thermal conductivity are achieved by utilizing the solution precursor plasma spray process to create inter-pass boundaries with a moderate overall porosity. Performance, efficiency, and emissions are compared against both a baseline configuration with a metal piston and an air-plasma spray “dense YSZ” coating. Experiments are carried out in a single-cylinder gasoline homogeneous charge compression ignition engine with exhaust re-induction. Experiments indicate that incorporating structured porosity into thermal barrier coatings produces tangible gains in combustion and thermal efficiencies. However, there is an upper limit to porosity levels acceptable for homogeneous charge compression ignition engine application because an elevated porosity fraction leads to excessive surface roughness and undesirable fuel interactions. Comparison of the coatings showed the best results with coating thickness of up to 150 µm. Thicker coatings led to slower surface temperature response and attenuated swing temperature magnitude.

The effects of boost pressure on stratification and burn duration of gasoline homogeneous charge compression ignition combustion

This article investigates the effects of intake pressure (boost) on the pre-ignition stratification and burn duration of homogeneous charge compression ignition combustion. Full cycle computational fluid dynamics simulations are performed with gasoline kinetics. An intake pressure sweep is performed while maintaining the same combustion timing and mean composition. The burn duration reduces with increasing boost, even though intake temperature is reduced to hold combustion timing constant. It is shown that the compositional stratification increases with boost whereas thermal stratification decreases. A quasi-dimensional model is employed to assess the effect of compositional stratification, pressure, mean temperature and isolate the effect of thermal stratification on burn duration. The analysis reveals that reducing charge temperature neutralizes the effect of increased boost on reactivity and the shorter burn durations at higher boost are primarily due to the lower thermal stratification. It is shown that higher pressures do not significantly increase the mixing and the lower thermal stratification is due to lower wall heat losses per unit charge mass. A follow-up set of non-reacting simulations with adiabatic walls corroborate this claim by revealing a constant magnitude of thermal stratification across the boost sweep.

Performance and emissions of gasoline Homogeneous Charge Induced Ignition (HCII) by diesel through whole operating range on a heavy-duty multi-cylinder engine

Recently the performance of dual fuel strategy on multi-cylinder engines over the whole engine map has received increasing attention. This research focuses on the potential of Homogeneous Charge Induced Ignition (HCII) combustion fueled with gasoline and diesel meeting Euro V emission standard through the whole operating range using a simple after-treatment system. This combustion mode utilizes a port injection of high-volatile fuel (gasoline) to form a homogeneous charge and a direct injection of high ignitable fuel (diesel) near the Top Dead Center (TDC) to trigger combustion. In this paper, an experimental and numerical investigation of the combustion characteristics and emission formation of HCII on a multi-cylinder heavy-duty engine is conducted. The effects of gasoline ratio (Rg), one of the most important parameters in dual-fuel mode, are explored and analyzed in detail. A Rg of 70–80% is recommended for better combustion and emission performance at the operating condition in this paper. HCII also turns out to be an effective strategy to reduce NOx and soot emissions at the same time. Furthermore, the high THC and CO emissions of HCII combustion can be eliminated using Diesel Oxidation Catalyst (DOC). Then the HCII strategy was optimized through the whole operating range showing a great potential of meeting Euro V limitations only with DOC as an after-treatment device. The fuel consumption also reduced with dual fuel strategy.

Effects of Direct Fuel Injection Strategies on Cycle-by-Cycle Variability in a Gasoline Homogeneous Charge Compression Ignition Engine: Sample Entropy Analysis

In this study we summarize and analyze experimental observations of cyclic variability in homogeneous charge compression ignition (HCCI) combustion in a single-cylinder gasoline engine. The engine was configured with negative valve overlap (NVO) to trap residual gases from prior cycles and thus enable auto-ignition in successive cycles. Correlations were developed between different fuel injection strategies and cycle average combustion and work output profiles. Hypothesized physical mechanisms based on these correlations were then compared with trends in cycle-by-cycle predictability as revealed by sample entropy. The results of these comparisons help to clarify how fuel injection strategy can interact with prior cycle effects to affect combustion stability and so contribute to design control methods for HCCI engines.

Particulate Characterization and Size Distribution in the Exhaust of a Gasoline Homogeneous Charge Compression Ignition Engine

Agglomeration, coagulation, surface condensation, adsorption and oxidation processes are a part of particulate evolution process and lead to significant changes in characteristics of particulate matter (PM), when they enter the atmosphere. PM formation can be significantly reduced by advanced combustion concepts such as homogeneous charge compression ignition (HCCI). In the present study, experiments were performed in a modified gasoline fuelled HCCI engine at varying intake air temperatures (T_i), exhaust gas recirculation (EGR) rates and relative air-fuel ratios (λ). For particulate characterization, a partial flow dilution tunnel was used to collect particulate samples on a filter paper. These particulate samples were analysed for benzene soluble organic fraction (BSOF), trace metals, and particulate morphology using scanning electron microscopy (SEM). Physical characterisation of particulates was done using engine exhaust particle sizer (EEPS), which measured the particle size-number distribution. In the experiments, higher PM was found for richer fuel-air mixtures and it further increased with application of EGR. Trace metals were found to be significantly lower for HCCI generated PM, which increased with increasing EGR. BSOF was negligible as compared to total PM which showed relatively lower toxicity of gasoline HCCI particulates. Total number of particles reduced with increasing λ, however particulate size-number distribution curve shifted away from accumulation mode, indicating that the particulate size decreased with increasing λ. Higher particle size-number distribution and particle size-mass distribution were observed for increasing T_i. Particulate surface area and volume also increased with increasing T_i and mixture strength.

Real-time internal residual mass estimation for combustion with high cyclic variability

In this work, a physics-based method of estimating the residual mass in a recompression homogeneous charge compression ignition engine is developed and analyzed for real-time implementation. The estimation routine is achieved through in-cylinder pressure and exhaust temperature measurements coupled with energy and mass conservation laws applied during the exhaust period. Experimental results on a multicylinder gasoline homogeneous charge compression ignition engine and dynamic analysis demonstrate the estimation routine’s ability to perform across a wide range of operating conditions as well as on a cycle-by-cycle basis for highly variable combustion phasing data.

Numerical simulation of cyclic variability in reactivity-controlled compression ignition combustion with a focus on the initial temperature at intake valve closing

Cyclic variations in dual-fuel reactivity-controlled compression ignition combustion were investigated using multi-dimensional simulations of a light-duty diesel engine. By comparing results with measured pressure traces from 300 consecutive cycles, it was found that the standard deviation of the 50% burn point in reactivity-controlled compression ignition combustion could be satisfactorily reproduced by monitoring the sensitivity of the 50% burn point to changes in initial in-cylinder temperature at intake valve closing in the simulations. Using this approach, the influences of fuel reactivity, diesel mass fraction, combustion mode, exhaust gas recirculation rate, intake pressure, and injection strategy on combustion stability were investigated. It was found that diesel/methanol reactivity-controlled compression ignition combustion exhibits larger cyclic variations than diesel/gasoline at the same operating conditions due to the lower reactivity of methanol. Compared to gasoline homogeneous charge compression ignition and diesel partially premixed combustion, diesel/gasoline reactivity-controlled compression ignition combustion showed the lowest cyclic variations for a given 50% burn point. When the 50% burn point was kept constant by adjusting the intake temperature, the introduction of exhaust gas recirculation and an increase in intake pressure resulted in decreased cyclic variations. Under the conditions tested in this study, with the employment of retarded injection timing, single injection, and increased injection pressure, the in-cylinder equivalence ratio becomes richer, which is helpful for the reduction in cyclic variations in reactivity-controlled compression ignition combustion. The overall results indicate that the present approach for describing cyclic variability is useful for practical applications.

Investigation on gasoline homogeneous charge compression ignition (HCCI) combustion implemented by residual gas trapping combined with intake preheating through waste heat recovery

Homogeneous charge compression ignition (HCCI) combustion achieved by residual gas trapping suffers from the limitation of the low load extension and fuel economy penalties whilst achieved by intake preheating alone is limited by the high intake thermal requirement and waste heat recovery. In the presented research, systematic engine experiments were carried out on a single cylinder engine on the combined use of residual gas trapping and intake preheating to achieve optimized combustion and better fuel conversion efficiency in the HCCI operational range. The effect of different combinations between residual gas trapping and intake preheating on HCCI combustion was explored and analyzed. It was indicated that the implementation transition from residual gas trapping to intake preheating significantly influenced the fuel economy and emissions. The decreased loss resulting from changed valve configuration contributed much more than half of the fuel economy improvement. The variation in emissions depended both on the combustion temperature influenced by dilution charge and the in-cylinder distribution affected by implementation form. It was also demonstrated that the increased benefit became less when the intake temperature further went up. Thus a relatively reasonable compromise between intake thermal demand and engine efficiency could be achieved to optimize the HCCI combustion by combining waste heat recovery and residual gas trapping. Compared to negative valve overlap method alone, the supplementary of intake preheating by waste heat recovery provided 8–12% fuel economy improvement throughout the typical load range of HCCI combustion. Also the low load boundary was effectively extended to 0.8bar, without suffering excessive increase in CO and HC emissions.

Performance and Emissions Characteristics of Diesel-Ignited Gasoline Dual Fuel Combustion in a Single-Cylinder Research Engine

Diesel-ignited gasoline dual fuel combustion experiments were performed in a single-cylinder research engine (SCRE), outfitted with a common-rail diesel injection system and a stand-alone engine controller. Gasoline was injected in the intake port using a port-fuel injector. The engine was operated at a constant speed of 1500 rev/min, a constant load of 5.2 bar indicated mean effective pressure (IMEP), and a constant gasoline energy substitution of 80%. Parameters such as diesel injection timing (SOI), diesel injection pressure, and boost pressure were varied to quantify their impact on engine performance and engine-out indicated specific nitrogen oxide emissions (ISNOx), indicated specific hydrocarbon emissions (ISHC), indicated specific carbon monoxide emissions (ISCO), and smoke emissions. Advancing SOI from 30 degrees before top dead center (DBTDC) to 60 DBTDC reduced ISNOx from 14 g/kW h to less than 0.1 g/kW h; further advancement of SOI did not yield significant ISNOx reduction. A fundamental change was observed from heterogeneous combustion at 30 DBTDC to “premixed enough” combustion at 50–80 DBTDC and finally to well-mixed diesel-assisted gasoline homogeneous charge compression ignition (HCCI)-like combustion at 170 DBTDC. Smoke emissions were less than 0.1 filter smoke number (FSN) at all SOIs, while ISHC and ISCO were in the range of 8–20 g/kW h, with the earliest SOIs yielding very high values. Indicated fuel conversion efficiencies were ∼ 40–42.5%. An injection pressure sweep from 200 to 1300 bar at 50 DBTDC SOI and 1.5 bar intake boost showed that very low injection pressures lead to more heterogeneous combustion and higher ISNOx and ISCO emissions, while smoke and ISHC emissions remained unaffected. A boost pressure sweep from 1.1 to 1.8 bar at 50 DBTDC SOI and 500 bar rail pressure showed very rapid combustion for the lowest boost conditions, leading to high pressure rise rates, higher ISNOx emissions, and lower ISCO emissions, while smoke and ISHC emissions remained unaffected by boost pressure variations.

Sequenced combustion characteristics, emission and thermal efficiency in gasoline homogeneous charge induced ignition

In this study, the concept of Homogeneous Charge Induced Ignition (HCII) is employed using port-injection of the high-volatile fuel (gasoline) to prepare in-cylinder homogeneous charge and direct injection of the high-ignitable fuel (diesel) near the top dead center (TDC) to control the start of combustion. The experiment was conducted on a single cylinder research engine with compression ratio of 16.7. The engine was operated at an engine speed of 1600rpm for the IMEP from 0.3 to 0.8MPa while the EGR was varied between 0% and 35%. Three different sequential heat release modes with HCII are studied, i.e., slow single-stage combustion (SSC), two-stage combustion (TSC) and fast single-stage combustion (FSC). The FSC mode is close to constant-volume combustion and the TSC mode is close to constant-pressure combustion. The FSC mode has high pressure rise rate and low thermal efficiency due to heat transfer. The TSC mode features high thermal efficiency and smoother pressure rise rate whereas the SSC mode should be avoided due to its high emissions of HC and CO and low thermal efficiency. TSC can be utilized for high load operation under the restricted conditions of peak in-cylinder pressure and combustion noise. NOx and soot emissions can be reduced significantly by using EGR for TSC. Heat release contribution of gasoline and diesel in dual-fuel combustion was distinguished by specially designed experiment. It is found that the first-stage heat release is from the local mixture of diesel and gasoline, and the second-stage heat release is from the premixed gasoline. As the diesel–gasoline ratio increases from 10% to 30%, the contribution of the first-stage combustion to the total heat release increases from 25% to 50% approximately in which the contribution from gasoline increases from 15% to 20%.

The effect of temperature and oxygen concentration on auto-ignition at low-load operating conditions in a gasoline homogeneous charge compression ignition engine

Homogenous charge compression ignition combustion offers significant efficiency improvements compared to conventional gasoline engines. However, due to the nature of homogenous charge compression ignition, traditional homogenous charge compression ignition combustion can be realized only in a limited operating range. Homogenous charge compression ignition operation in the high-load range is limited by the trade-off between excessive combustion noise and deteriorated combustion stability. The low-load operation of homogenous charge compression ignition combustion is limited by combustion instability. In order to understand the auto-ignition characteristics at low-load operation, the effect of negative valve overlap, injection timing and external exhaust gas recirculation was investigated. These parameters have a significant impact on temperature and oxygen concentration of the mixture and thus the auto-ignition characteristics. To help interpret the results, an auto-ignition integral calculation was developed and verified with experimental data. It is confirmed that the newly developed auto-ignition integral predicts well the ignition timing and can be used to interpret experimental observations. It is found that at a given speed and load, there is an optimum combination of negative valve overlap and injection timing for stable auto-ignition. When the amount of reforming is low, the in-cylinder temperature is not high enough for auto-ignition. This causes delayed auto-ignition phasing (unstable combustion). When the amount of reforming is high, the cyclic variability of reforming increases, which leads to instability of the main combustion event. When exhaust gas recirculation is employed, the amount of reforming does not change, thus the combustion instability is caused by lack of oxygen concentration rather than lower in-cylinder mixture temperature.

Adaptive control of homogeneous charge compression ignition engines

SUMMARYThis paper presents an adaptive controller, which maintains consistent ignition timing control of a gasoline homogeneous charge compression ignition engine with high dilution in the presence of uncertainty or unknown variation in plant parameters such as exhaust runner wall temperature and cylinder charge properties. The control of the combustion timing is based on manipulating the charge temperature through internal dilution, which is achieved by controlling the lift of a secondary opening of the exhaust valves, also known as the rebreathing lift. The adaptive controller is designed on the basis of a simplified bilinear parametric model, which contains only the cycle‐to‐cycle combustion timing dynamics. Implementation of the designed adaptive controller involves feedforward of the injected fuel and feedback of the combustion timings CA50 and CA90 when 50% and 90% of energy are released, respectively, which alleviates the impact of inevitable errors in estimation of in‐cylinder charge properties such as temperature, pressure, and compositions. It is shown through convergence analysis and closed‐loop simulation of a full‐order engine model that the adaptive controller is able to drive the combustion timing CA50 to desired set points by stabilizing the bilinear dynamics when plant parameters are changing. Copyright © 2013 John Wiley & Sons, Ltd.

Comparative study on Gasoline Homogeneous Charge Induced Ignition (HCII) by diesel and Gasoline/Diesel Blend Fuels (GDBF) combustion

Gasoline Homogeneous Charge Induced Ignition (HCII) by diesel uses port fuel injection of gasoline to form a homogeneous charge and direct injection of diesel fuel as an ignition source. Gasoline/Diesel Blend Fuels (GDBFs) uses a premixed blend of diesel and gasoline which is directly injected into the cylinder for combustion. Exploratory studies show that these two ways may integrate the advantages of gasoline and diesel fuels to achieve high thermal efficiency and low emission targets. Combustion characteristics, emission characteristics, thermal efficiency and adaptability of low-temperature combustion in these two combustion modes have been comparatively investigated on a high-pressure common rail single-cylinder diesel engine. The results show that both HCII and GDBF modes can achieve higher thermal efficiency than gasoline SI combustion and a similar or even higher thermal efficiency than diesel CI combustion because the combustion was closer to constant volume combustion. As gasoline ratio increases, the fuel–air mixing is improved in both HCII and GDBF modes, and thus soot emissions reduced dramatically, with a biggest reduction of 90%. The ignition delay in HCII mode remained almost the same, while the ignition delay in GDBF mode increased significantly with the increase of gasoline ratio. As gasoline ratio increases, the combustion duration in both HCII and GDBF modes shortened significantly. Both HCII and GDBF modes can achieve low temperature combustion with extremely low soot and NO emissions when combined with large amounts of EGR. These modes demonstrate an advantage over the diesel CI combustion mode, where the NO emissions decreased and soot emissions increased with the increase of EGR, exhibiting the classical NO-soot trade-off.

Extension of an operating load range of a four-cylinder gasoline homogeneous charge compression ignition engine via a blowdown supercharge system, aiming at in-cylinder thermal stratification

In order to extend the operational range with a gasoline fueled multi-cylinder homogeneous charge compression ignition engine, a blowdown supercharge system and an exhaust gas recirculation guide was developed. The concept was to provide a large amount of diluted mixture and a strong in-cylinder thermal stratification for decreasing nitrogen oxide emissions and pressure rise rate during high-load homogeneous charge compression ignition operation. Secondary air injection was also proposed to reduce a cylinder-to-cylinder variation in ignition timing, which is one of the limiting factors of multi-cylinder homogeneous charge compression ignition operation. In advance of experimental works, the blowdown supercharge system and the exhaust gas recirculation guide were proved to be effective to reduce pressure rise rate for high-load operation using three-dimensional in-cylinder flow simulations and zero-dimensional multi-zone simulations with detailed chemical kinetics. Based on the simulation results, experiments were conducted using a slightly modified production four-cylinder gasoline engine. At first, the effects of the proposed techniques were experimentally investigated by focusing on one cylinder out of four. Then, a four-cylinder homogeneous charge compression ignition operation test using the new techniques was carried out. The one-cylinder measurements revealed that the blowdown supercharge system with an exhaust gas recirculation guide is capable of extending the homogeneous charge compression ignition operating range up to a net indicated mean effective pressure of 590 kPa for naturally aspirated conditions. In addition, secondary air injection was experimentally demonstrated as a technique for reducing a cylinder-to-cylinder variation in ignition timing. Reducing the cylinder-to-cylinder variation in ignition timing, four-cylinder homogeneous charge compression ignition operation with a net indicated mean effective pressure of 570 kPa was successfully achieved with the blowdown supercharge system and the exhaust gas recirculation guide.

Improvement of thermal efficiency of a four-cylinder gasoline homogeneous charge compression ignition engine via blowdown supercharging

The objective of this study is to develop a practical technique to achieve homogeneous charge compression ignition operation with a wide operating range using a blowdown supercharge system, which has been previously demonstrated as an effective technique to extend the upper load limit of acceptable homogeneous charge compression ignition operation. The valve actuation strategy to attain acceptable homogeneous charge compression ignition operation in a wide operating range has been newly developed and experimentally examined. The proposed strategy provides high in-cylinder temperature and a relatively small amount of in-cylinder mixture during low-load operations to improve the combustion stability while providing a large amount of diluted mixture for high-load operations to keep the in-cylinder pressure rise rate and nitrogen oxide emissions low. In addition, thermal efficiency and exhaust emissions for various homogeneous charge compression ignition operating loads using the blowdown supercharge system were experimentally investigated. Experimental results showed that the proposed valve actuation strategy, in which early intake valve closing and relatively late exhaust gas recirculation valve opening occurred, was effective to increase combustion stability during low-load conditions, and a stable homogeneous charge compression ignition operation at a net indicated mean effective pressure of 140 kPa was achieved. Compared to conventional spark-ignition operation, 14% to 35% improvement in brake specific fuel consumption rate was attained with more than 99% reduction in nitrogen oxide emissions for homogeneous charge compression ignition operation using the blowdown supercharge system.

HC2-4 Comparison of gasoline homogeneous charge induced ignition (HCII) by diesel and gasoline/diesel hybrid fuel (GDHF)(HC: HCCI Combustion,General Session Papers)

HC2-4 Comparison of gasoline homogeneous charge induced ignition (HCII) by diesel and gasoline/diesel hybrid fuel (GDHF)(HC: HCCI Combustion,General Session Papers)

Investigation of the potential of corona ignition to control gasoline homogeneous charge compression ignition combustion

A complex task regarding the control of the homogeneous charge compression ignition (HCCI) combustion process is the control of combustion timing, represented by the crank angle at which 50 per cent of the fuel mass inside the cylinder is burned (MFB50). The most important parameters for transient MFB50 control are the mass of (hot) residual gas inside the cylinder (e.g. retained by internal exhaust gas recirculation), the injection strategy (in the case of direct fuel injection), and the spark timing. In this paper, the potential of a corona ignition system is examined in comparison with a conventional spark ignition system for the HCCI combustion process. For this purpose, thermodynamic investigations have been carried out on a single-cylinder research engine, combined with one-dimensional gas exchange analyses and high-speed visualization of combustion in a transparent engine. It could be demonstrated that both ignition systems are capable of influencing the autoignition process. The corona ignition system, however, allows a much later ignition point for achieving the same MFB50. This is due to the spatial character of the initial ignition area of corona ignition. In addition, the corona ignition system is more robust with respect to a change in the boundary conditions, such as a variation in the residual gas rate or the mixture composition. It is therefore more reliable in initiating autoignition, even in critical operating conditions. Additionally, it was found that the corona ignition system permits the combustion to be influenced by means of a variation in the ignition energy, which appeared to be not the case for the conventional ignition system.